In the evolution of automotive design, great importance has recently been placed on automotive safety and ergonomics. Modern automobiles are provided with many safety systems to protect both the vehicle itself and its passengers in the event of a collision. Among such safety systems is the supplemental passenger restraint system for the front seat occupants of the vehicle. This system often times referred to as an airbag system, is provided in the hub of the steering wheel for the vehicle driver and occasionally, at the right hand end of the vehicle's instrument panel for the front seat passenger.
In the case of the driver's side supplemental restraint system, the hub of the steering wheel houses an airbag, a rapidly combustible material which when burned, gives off gasses which inflate the bag and an ignition system for initiating the combustion. The hub is covered by a soft, frangible, flexible cover which tears open under the force of airbag inflation, thereby allowing the bag to fill the area of the passenger compartment between the driver and the steering wheel as the bag inflates. The flexibility of the cover contributes to the frangibility thereof, provides a soft shock absorbing surface to reduce the risk of injury during minor incidents in which the airbag does not deploy, and provides an aesthetically pleasing extension of the colors and textures employed in other parts of the vehicle's passenger compartment.
One of the primary goals of modern ergonomic vehicle design is to provide controls which are conveniently accessible to the driver with a minimum of diversion of the driver's attention from the road. Since the vehicle's accessories are for the most part manually actuatable and operable, such accessories are conveniently operable from the steering wheel itself. Historically, horn buttons (switches) were positioned at the center of the steering wheel and studies have shown that drivers which are not completely familiar with the operation of a vehicle will instinctively reach for the center of the steering wheel when they wish to operate the horn. However, prior art horn buttons which employ hard mechanical components therein are not conducive for use with steering wheels having flexible airbag covers. Thus, automotive interior designers have been forced to move horn buttons to the spokes of the steering wheel and in some cases, to stalks extending outwardly from the steering column. Both locations have been found to be more inconvenient from the standpoint of the driver, than the center of the steering wheel. Furthermore, as time goes on, automobiles are provided with ever greater numbers of electrical accessories. Present day automotive designers continue to look to the steering wheel as a location for mounting the switches and controls for such accessories. By way of example, U.S. Pat. No. 4,628,310 to Reighard, et al discloses a multi-function steering wheel which includes controls for such accessories as headlights, windshield wipers, cruise control and the like. Clearly, such large numbers of accessory switches and controls cannot be accommodated within the limited area of the steering wheel spokes.
For safety reasons, the switches and controls for such accessories, are unsuitable for use with steering wheels provided with the soft supplemental restraint system cover. Hard components would seriously compromise any ability of the steering wheel cover to protect the driver from impact injuries and indeed could actually cause injury if fragmented or released as projectiles from the airbag cover upon deployment of the airbag.
Certain prior art airbag systems have been mounted above a conventional horn switch so that when it is desired to actuate the horn, the entire airbag system is depressed. Such a system requires rather large clearances between the movable airbag system and the steering wheel hub to minimize the risk of interference to the required movement of the components. Such clearances contribute to the complexity of the system and detract aesthetically therefrom.
Accordingly, an improved scheme for providing control signals to electrical accessories within the environment of a steering wheel provided with a supplemental restrain system, is desirable. Any apparatus employed in such a scheme must be required to withstand the extreme temperatures encountered in automotive interiors and should be sensitive enough to respond to moderate input forces, yet not so sensitive as to produce false signals in response to normal vibration or temperature changes.